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1 September 2013 Implications of Cutthroat Trout Declines for Breeding Ospreys and Bald Eagles at Yellowstone Lake
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Abstract

In Yellowstone National Park (YNP), Ospreys (Pandion haliaetus) feed primarily on cutthroat trout (Oncorhynchus clarki bouvieri) and cutthroat trout represent approximately 23% of prey consumed by Bald Eagles (Haliaeetus leucocephalus) during the breeding season (Swenson 1978, Journal of Wildlife Management 42:87–90; Swenson et al. 1986, Wildlife Monographs 95:3–46). The introduction of exotic lake trout (Salvelinus namaycush) to Yellowstone Lake during the late 1980s caused substantial declines in populations of cutthroat trout. Historically, more than half of all breeding pairs of Ospreys and Bald Eagles in YNP have nested near and foraged at Yellowstone Lake and the decline in cutthroat trout numbers may affect rates of reproduction for these two species. We studied the relationship between an index of cutthroat trout abundance and spring weather on Osprey (1987–2009) and Bald Eagle (1987–2007) reproduction. We documented steep declines in an index of cutthroat trout abundance, Osprey productivity and nesting success, and a dramatic decline in the number of Osprey breeding pairs. Bald Eagle productivity and nesting success also declined, but at a slightly slower rate than that of Ospreys, and the number of breeding pairs of Bald Eagles increased over the study period. Osprey reproduction was positively correlated with an index of cutthroat trout abundance and spring temperatures. However, the relationship between Bald Eagle reproduction and the index of cutthroat trout abundance was unclear. Our study suggested that the recovery of cutthroat trout is important to maintaining a breeding population of Ospreys at Yellowstone Lake, but may be less important for the Yellowstone Lake Bald Eagle population.

En el Parque Nacional Yellowstone, Pandion haliaetus se alimenta principalmente de truchas de la especie Oncorhynchus clarki bouvieri y estas truchas representan aproximadamente el 23% de las presas consumidas por individuos de Haliaeetus leucocephalus durante la época reproductiva (Swenson 1978, Journal of Wildlife Management 42:87–90; Swenson et al. 1986, Wildlife Monographs 95:3–46). La introducción de una especie de trucha exótica (Salvelinus namaycush) en el Lago Yellowstone durante la última parte de la década de 1980 causó disminuciones substanciales en las poblaciones de O. c. bouvieri. Históricamente, más de la mitad de todas las parejas reproductivas de P. haliaetus y H. leucocephalus han anidado y forrajeado en el Lago Yellowstone y la disminución en los números de O. c. bouvieri podría afectar las tasas reproductivas de estas dos especies. Estudiamos la relación entre el índice de abundancia de O. c. bouvieri y el clima de primavera sobre la reproducción de P. haliaetus (1987–2009) y H. leucocephalus (1987–2007). Documentamos marcadas disminuciones en el índice de abundancia de O. c. bouvieri, en la productividad y en el éxito de anidación de P. haliaetus, y una dramática disminución en el n

The Raptor Research Foundation, Inc.
Lisa M. Baril, Douglas W. Smith, Thomas Drummer, and Todd M. Koel "Implications of Cutthroat Trout Declines for Breeding Ospreys and Bald Eagles at Yellowstone Lake," Journal of Raptor Research 47(3), 234-245, (1 September 2013). https://doi.org/10.3356/JRR-11-93.1
Received: 16 December 2011; Accepted: 1 January 2013; Published: 1 September 2013
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